AuthorTopic: Speaker protection attentuator (Read 1237 times)

Okay, here comes an unusual question, that will demand some explanation. I run an MP-1 with a Marshall 9040 solid state amp. After having tried some different speakers I have come to the conclusion that I love everything about the regular Celestion Greenbacks… except the 25 watt rating. The speakers really come to their own when they are really being pushed, but since a little bit of extra headroom is advisable with solid state power amps, one runs the risk of running them too hard. Therefore: are there any devices out there that can either attenuate the signal before it reaches the speakers, if its power exceeds a certain limit? or something that at least could give a warning?

Hey Sirion, the idea of headroom in the amp(s) compared to speaker power handling is more suited to PA AND you need to know what you are doing (and generally you have a compressor set to peak limit before the amps). Comparatively, distorted guitar is very compressed(ish) and better (IMHO) to have a bit more speaker capacity than amp, not that you can't do it, just have to be careful not to pop speakers . It doesn't help that the 9040 has no vol knobs... So you choices are to:control it with speaker impedance and/and numbers of (25w) speakersuse a compressor/peak limiter before the ampuse a power soak between amp and speakers (I have a Tom Shultz power soak I use with my 73 Marshall 50, not for the speakers though, just so I can be in the same room )

To do it with speakers, depends how many 25w greenbacks you have per channel and their impedance. IIRC the Marshall can deliver 120w p/ch into 4 ohms but will be less into 8 or less again into 16 ohms.So Ideally give it a 8 ohm load with 4 x 25s, nice and safe (but that's 2 quad boxes)or 16 ohm load, and 2 x 25 w greeenies (p/ch) and be a "bit" careful how high you turn up the input to the amp.It will also be ok at 8 ohms, but you need to be even more careful

Another thought, you can put a fuse in the speaker box, there used to be this great PA bible book that had the correct fuse ratings, maybe MJMP can tell you the right value fuses to use ? Or maybe these days there are circuit breakers you can use for the same job .

And you "could say" run just 1 x 25 w 16 ohm per side, it will sound f**king awesome , but popping a speaker becomes a real likely hood (as I found out when I was 14...crap it sounded so good though (well up to the point where there was no sound LoL), that was with Philips 12" twin cone 20w hifi speakers, my dad was not impressed ).

I agree on not using a fuse for protection; it'll easily slow-down your attack.As you amp has no master volume control, a simple voltage divide could be installed, set to limit the max power the amp can produce.

Else, as has been suggested, use a limiter. I'll object to using a compressor; you'll want to only limit the too hot peaks.

Check my short story on the Gemini compressor/limiter; it's pretty neat, and can be set to hardly be noticeable or to outright do something to the sound, should you fancy..

Mmmm using a fuse to protect your speakers isn't such a good idea IMO. Maybe use a limiter between preamp and poweramp?

Having a fuse between the poweramp and speakers "might" seem like a good idea, but in reality it's a very bad idea if you're using a tube poweramp or any amp with a tube power section. If the fuse blows, you've just unloaded the output transformer (just like not having a speaker load connected) and that also goes poof. S.S. power sections are a little more forgiving of that, but....

As MJMP says, a limiter in there would probably be your best bet. Better yet, pay close attention to your overall volume levels. If the speakers are making noises that they normally shouldn't, back the overall volume down. There is a fine line between getting the speakers to bark a little bit with the right amount of power (especially lower-wattage rating speakers) and just overpowering them and burning them up. Once you get some "bark" out of them, applying more power certainly won't make them sound better.

Thanks for the replies! It is awesome that there actually exists a forum with this sort of competence! (I tried at some other, very good forums, and got virtually nothing) I think I have found what I need: